1. Field of the Invention
The present invention relates to a percussion instrument of the type utilized in dental practice for determining the degree of looseness of teeth in the gum tissue- and in particular to such a percussion instrument having a ram which is accelerated from a rest position to a defined speed by the application of a force thereto and is moved toward a test subject such as a tooth in free flight with a constant velocity, and which returns to its initial position by the application of a magnetic field.
2. Description of the Prior Art
A percussion instrument having a displacably seated ram which is accelerated to a specific speed toward a test object by means of a spiral spring disposed in a front portion of the instrument containing the test head, and which is held in its initial position by means of a magnetic coil is disclosed in German OS No. 2,617,779. After complete relaxation of the spring, the ram separates from the spring and, conducted by means of bearings, proceeds in free flight toward the object to be tested with a theoretically constant speed. After impact against the test object, the ram is repelled in the direction toward its initial position by the reactive counter force arising as a result of the impact. The coil is subsequently supplied with a current pulse at the end of the return motion of the ram. The ram is returned to its initial position by the magnetic field generated thereby and the spring is again tensioned. An acceleration pickup connected to the ram by a flexurally slack cable detects a change in the ram velocity upon impact of the ram against the object. During the excursion and return motion, this change of velocity at the object can be evaluated for specific test and diagnostic purposes by means of an evaluation electronics unit connected to the acceleration pickup.
In dental practice, for example, for detecting tooth mobility, that is, the degree to which a tooth is loose, the time within which, after occurrence of the pulse by the ram, the tooth to be tested is subjected to an impact by the ram at a theoretically known velocity and the time within which the ram returns to its initial position is a measure of the degree of looseness of the tooth in the gum tissue.
In conventional devices of the type described above, the front portion of the instrument, from which the ram having a test head attached thereto emerges, is relatively large in diameter due to the spring arrangement. Working with such an instrument, particularly in dental practice, is thus rendered difficult. Another significant disadvantage associated with instruments of the type described above, is that when the instrument is applied to the test subject at an attitude deviating from the horizontal, the velocity of the ram is influenced by the accelerating force of gravity, which can result in falsification of the test results.
Another disadvantage of conventional percussion instruments is that the connecting lines attached to the acceleration pickup, and thus participating in the ram motion, can easily tear when the ram is twisted. The use of anti-twist devices connected to the ram in conventional percussion instruments result in undesired additional friction forces.